feat!(mcp-adapters): add authProvider for oauth, fix header passing

[benjamincburns]

BREAKING_CHANGE: Drops the useNodeEventSource flag and stops passing an empty eventSourceInit object to Streamable HTTP and SSE transport constructors. If there continues to be header passing issues as a result of the way SSEClientTransport and StreamableHTTPClientTransport handle EventSource initialization, the correct fix will be to PR a change to the MCP SDK that changes how headers are populated on EventSource initialization.

Also includes integration tests that validate the new behavior against actual MCP servers, and fixes to further problems surfaced by these tests related to passing headers when authProvider is present.

fixes #8196
fixes #8194

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
langchainjs-docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 28, 2025 0:00am

1 Skipped Deployment

Name	Status	Preview	Comments	Updated (UTC)
langchainjs-api-refs	⬜️ Ignored (Inspect)			May 28, 2025 0:00am

[Copilot]

Pull Request Overview

This PR introduces OAuth 2.0 support by replacing the useNodeEventSource flag with an authProvider option and updates header passing and error messaging for both Streamable HTTP and SSE transports. Key changes include:

• Removing the useNodeEventSource flag and replacing it with authProvider in the transport schemas and client functions.
• Updating error messages to specifically handle authentication failures.
• Enhancing documentation and test coverage to demonstrate OAuth integration and header management.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
libs/langchain-mcp-adapters/vitest.setup.ts	Removed the file that mocks node:crypto, suggesting tests now use real implementations or other mocks.
libs/langchain-mcp-adapters/vitest.config.ts	Updated configuration formatting (double-quoted strings) without functional changes.
libs/langchain-mcp-adapters/src/client.ts	Refactored transport creation to support OAuth via authProvider, updated error messaging, and adjusted reconnection options.
libs/langchain-mcp-adapters/tests/fixtures/dummy-stdio-server.ts	Added a dummy stdio server for integration testing.
libs/langchain-mcp-adapters/tests/fixtures/dummy-http-server.ts	Enhanced the dummy HTTP server to support header and authentication testing.
libs/langchain-mcp-adapters/tests/client.comprehensive.test.ts	Modified tests to expect updated transport configuration with authProvider support.
libs/langchain-mcp-adapters/README.md	Updated guides to reflect the new OAuth authentication option and removed outdated sections.
libs/langchain-mcp-adapters/.eslintrc.cjs	Minor ESLint config improvements using path.join for tsconfig paths.

Comments suppressed due to low confidence (2)

libs/langchain-mcp-adapters/vitest.setup.ts:1

• Confirm that the removal of vitest.setup.ts is intentional and that any necessary mocking of node:crypto is now handled elsewhere.

Entire file removal

libs/langchain-mcp-adapters/src/client.ts:1057

• The _createNodeEventSourceTransport function now returns a StreamableHTTPClientTransport instance instead of an SSEClientTransport, which may not be intended. Consider returning an SSEClientTransport to meet the expected type for SSE connections.

return Object.keys(options).length > 0 ? new StreamableHTTPClientTransport(new URL(url), options) : new StreamableHTTPClientTransport(new URL(url));

[nfcampos]

Thanks!